Reformer flue gas tunnel and refractory components therefor

ABSTRACT

A refractory block for a steam reformer furnace tunnel includes a hollow main body, at least one first mechanical mating member defining a protruded portion extending from an upper surface of the main body, at least one second corresponding mechanical mating member defining an opening corresponding to the protruded portion formed in a portion of a lower surface of the main body, at least one third mechanical mating member defining a tab provided in a portion one of a first end and an opposed second end or a first side and an opposed second side of the main body, at least one fourth mechanical mating member comprising a groove formed in the other of the first end and the second end or the first side and the opposed second side of the main body, and at least one cavity formed in the lower surface of the main body.

FIELD OF THE INVENTION

The present invention relates to a refractory tunnel, also known as areformer flue gas tunnel, for a hydrogen reformer furnace for use insteam methane reformer processes, and refractory components therefor.More specifically, the present invention provides a light-weight,free-standing tunnel structure, without the use of mortar, that betterwithstands the application of hydrogen reformers, using refractorycomponents having a more mechanically robust design and made of higherperformance material than that which has been used heretofore.

BACKGROUND OF THE INVENTION

A hydrogen reformer furnace converts natural gas into hydrogen through aseries of catalytic reactions. One of the most prevalent routes for theconversion of methane (CH₄) to petrochemicals is either through themanufacture of hydrogen, or a mixture of hydrogen and carbon monoxide.This hydrogen/carbon monoxide material is referred to as “Synthesis Gas”or “Syngas.” Indeed, steam methane reforming (SMR) of natural gas orsyngas is the most common method of producing commercial bulk hydrogenas well as hydrogen that is used in the industrial synthesis of ammonia.At temperatures around 1000° C., and in the presence of metal-basedcatalysts, steam reacts with methane to yield carbon monoxide andhydrogen. These two reactions are reversible in nature:

CH₄+H₂O⇄CO+3H₂

The reaction is endothermic and requires the input of large amounts ofheat in order to be sustained. Heating gas accounts for 80% of the totalprocess gas requirement.

A common type of hydrogen reformer furnaces is known as a “top down,” or“down fired” furnace. FIG. 1 is a perspective cut-view of a conventionalhydrogen reformer furnace 800. Natural gas burners (not shown) arespaced at the top of the furnace 800 in between rows (also known aslanes) of catalyst pipes 70, and produce heat through combustion. Theburners fire downward, parallel to the hydrocarbon-steam mixture flow,direction through the catalyst tubes 70, which are centrifugally castchrome-nickel tubes that are typically 10-40 feet long, and mountedvertically in the furnace 800. The tubes 70 contain an activated nickelcatalyst on alumina carriers in the form of pellets or balls, forexample. The process gas and steam are fed downward over the catalystand removed from the bottom of the tubes 70.

The primary reformer operates at temperatures in the 700-800° C. range.The hot gas is then passed into a convective heat transfer zone, andsteam is generated and may be fed back into the primary reformer. Thisunit is used to produce synthetic fuel that may be turned into a varietyof liquid fuels for powering internal combustion engines. It is alsooften used to produce hydrogen for other processes in the plant burnerwhereby flame and hot gas radiation provide heat input to the tubes tosupport the highly endothermic reaction. The air exits out one side ofthe bottom of the furnace 800. Based on the location of the burners andthe furnace exit, the air flow and heat distribution are non-uniform. Inthis situation, it is common for the hot gasses with flow directly tothe exit, creating a cold area in the back of the unit and a hot spotjust before the exit which can reach temperatures high enough to damagethe catalyst tubes. In order to correct for this, flue gas tunnels 80are provided, which act as collection ducts for the combustion gases,promoting even heat distribution in order to improve efficiency andprolong the life of the tubes 70.

While SMR is a well-established process, and efforts have been made overtime to optimize many facets of the technology in order to increaseefficiency, most of the focus has been centered on improving aspects ofthese reformers with respect to the catalyst, metal alloys, burners,feed stocks, etc. However, one piece of SMR technology has beencompletely ignored where advancements are concerned. That is, therefractory designs used in the construction of these units have remainedstagnant for decades. In particular, the flue gas tunnels whichtransport combustion gasses through the fired heaters have not beenchanged despite the clear need for improvement based on performancereliability issues.

These tunnels 80 average about 8 feet in height, 3 feet in width and runthe full length of the furnace unit 100 (e.g., 40 ft-50 ft). Because ofthe size of these tunnels 80 and the volume of refractory materials usedin their construction, they have traditionally been fabricated usingbasic brick shapes (e.g., standard rectangular shapes, shown in FIG. 2),in a similar manner to constructing any structural brick wall. The walls81 of the tunnels 80 are then topped with a series of rectangular blocks82 that form a lid (see, e.g., FIGS. 1-3). Historically, conventionaltunnel walls 81 have been very prone to mechanical failure under heatand over time. The main modes of failure for these flue tunnels arerelated to refractory design, installation technique, mechanical abusein service, and initial material selection.

Even though they are problematic, these tunnels 80 are essential inorder for the furnace unit 800 heat evenly and achieve the requiredefficiency. For example, if a down fired reformer did not include suchtunnels 80 in its unit construction, all of the combustion gasses wouldrush into the flue at the exit of the reformer. This would create uneventemperatures throughout the unit with cold areas away from the flue andhot spots near the exit of the unit, as discussed above. As a result,the reformer would not only experience reduced efficiency, but wouldalso overheat the catalyst tubes near the exit, causing prematurefailure to occur.

The design and construction of conventional flue gas tunnels 80 in SMRsinvolves the use of flat bricks with typical dimensions of 3 in×9 in×6.5in. The walls 81 are constructed so that half blocks are left out inregular patterns to allow for gas passage through the wall 81 into thetunnel 80 (not shown). Typically, the bricks are mortared in placeduring construction in order to hold the walls 81 together. A commonalternative to the standard flat brick is a standard tongue and groovebrick 83, 84 (see, e.g., FIGS. 4 and 5). While many sizes andconfigurations of these types of bricks exist, such conventional brickstypically use a simple tongue and groove feature to mechanically engageeach other when vertically stacked in the common manner. As shown inFIGS. 4 and 5, conventional bricks 83, 84 include simple tongue 832, 842and groove-style mating features 833, 843 that fit together whenvertically stacked.

In the past, in conventional tunnel structures, large expansion gapshave been provided, located every 6-10 ft along the tunnel walls inorder to account for thermal expansion in the system. The expansion gapis a critical aspect of design and construction, because the anticipatedthermal growth must be accommodated. In this case, however, due to thepresence of these large expansion gaps, every tunnel is actually made upof several large free-standing walls. In order to help support thesefree-standing sections of tunnel wall, intermediate support walls orpilasters are therefore also provided (not shown). These intermediatesupport walls connect the outer walls of tunnels between catalyst tubesin order to prevent the walls from leaning or collapsing. Pilasters,also known as buttresses, serve the same purpose, and are structured ascolumns of bricks located outside of the tunnel walls (not shown).

Another feature of the tunnel wall construction is the end wall (notshown). Also known as cross-over walls or target walls, these brick wallsegments connect tunnels at the exit of the unit, preventing gas by-passthrough the surrounding lining. In addition to providing additionallateral support, the end walls also ensure that all combustion gassesproperly exit through the flue gas tunnels 80.

Once the tunnel walls are constructed, the tunnel covers (lids) areplaced on top. These covers, often called coffin covers, are typicallymade from large slabs of refractory material. However simple the designmay be, they serve an important purpose, because failed covers decreasethe unit efficiency, cause tunnel wall failure as they fall, andcontribute to shorter tube life. There are four main styles of coffincovers. The main style is a rectangular or square solid design (see,e.g., lid 82 in FIG. 3). This represents the traditional approach, andis simply a solid slab of refractory material that spans the horizontaldistance (gap) between walls 81. These solid covers 82 can also have anotched surface or otherwise be formed with a mating feature on thebottom or sides that can mechanically engage with the tunnel walls andprovide additional support (not shown). Another style is the hollow orextruded lid 821 (see, e.g., FIGS. 6 and 7). These types of covers 821have the same outer dimensions as the rectangular solid lid 82, butinclude a pair of hollowed-out sections (cavities) 822 in the middle toreduce the weight of the lid and the resulting stresses.

Another common cover design is the off-set cover 831, as shown in FIG.8. This solid lid features a slanted geometry that facilitatesengagement between adjacent covers, which offers extra support duringupsets and which can help support cracked lids in the event of a coverfailure. FIG. 9 shows a tongue and groove cover 851, which is a anotherversion of the off-set cover 831, but whose mechanical mating features(i.e., tongue 851 a, and groove 851 b) provide even more engagement withadjacent lids 851.

One of the current types of failures seen in the field is the collapsingof a section of lids, or all of the lids, over the entire length of thetunnel. Once installed, the lids act as a beam, and a crack in themiddle of the lid is often the result of the ratio between the span andthe material thickness. The cross-section (thickness) of the replacementlids is then increased, but after another campaign, the failure istypically even worse than before. This is because the lid failure is nota result of static load. Hand calculations coupled with computersimulation have shown that the static load alone imparts very littlestress on the lids, and will not result in a failure. Computer runfinite element analysis (FEA) of a 9 in W×9 in T×42 in L solidrectangular lid (see, e.g., FIG. 3) installed on a tunnel at a constantservice temperature of 1900° F. demonstrated that the lid has noexternal forces acting upon it other than its own weight. The result isa maximum stress of a very modest 10 psi.

With many materials, the modulus of rupture (MOR) decreasessignificantly at higher temperatures, and it is possible to select a lowgrade refractory lid material whose MOR decreases at operationalexcursion temperatures to a point that even the mild stresses associatedwith the static load can result in failure. However, most engineeredrefractory material suppliers characterize the hot modulus of rupture(HMOR), and supply a material option for lids that have a high enoughHMOR so that even with the decrease in strength, the static loads stillhave a very significant factor of safety associated therewith. Based onthe comparison of the FEA results to the published HMOR, it has beenconcluded that most lid failure is not a result of static load alone,and is therefore a result of stresses associated with the thermal state.

Thermal stresses in such a situation manifest several ways. One way thecomponents can fail is if the thermal expansion is not properly managed,resulting in excessive compressional force. Since the lids are placed ontop of the wall sections and the only constriction is either friction ormortar, the thermal expansion will not be constricted to the point offailure. The HMOR of commonly used refractory mortars is roughly 500psi, well below that of the refractory material selected for the tunnellid, so if the thermal stresses reach that level, the mortar will breakand the lid will be free to expand as necessary.

The component can also fail as a result of thermal stress that occurs asa result of any temperature differential incurred during operation, andis not limited to instances of large upsets. Thermal stress failureresults when the thermal expansion from one area of a component isdifferent from another area resulting in a stress greater than the yieldstrength of the material. If the temperature in the convection sectionof the furnace is different than the temperature inside the tunnels,even for a short period of time, the potential for thermal stress ispresent. FEA of a 9 in W×9 in T×42 in L solid rectangular lid (see,e.g., FIG. 3) installed on a tunnel with a temperature on the topsurface of the lid at 1910° F. and a temperature on the bottom surfaceof the lid at 1900° F. has shown that the lid has no external forcesacting upon it, other than its own weight. A differential temperature of10 degrees across the lid results in a max stress of 1500 psi, which isabove the HMOR of lower end refractory materials. In a situation where avery large number of the lids of a tunnel all failed during the samecampaign without any of the walls collapsing, it is most likely that themode of failure was thermal stress.

Another important factor in the performance of the tunnel lids is thematerial's creep resistance. Creep occurs when a material slowly butpermanently deforms under long term exposure to high levels of stressthat are below the material yield strength. The result on the tunnelwalls is a transmission of the lids mass in the vertical direction,which compliments the strength and structure of the wall. Creep of a lidwill result in a “sagging” of the center span and will change theinteraction force between the lid and the tunnel walls, and eventuallylead to a failure. Creep can be characterized with ASTM standardtesting, which is representative of the use of a tunnel lid in serviceand is an important component to material selection. ASTM tests on SuperDuty Brick have published results of a 7.86% deflection at 2,600° F. Theresult on the tunnel walls is a transmission of the lids mass at anangle that is a few degrees off of the vertical axis and whichencourages the walls to separate further apart from one another at thetop than at the bottom.

A full tunnel collapse can actually be the result of several differentmodes of failure. Conventional tunnel construction uses hundreds ofthousands of pounds of refractory brick and lids, all of which accountsfor mass that ultimately rests on a final base layer of insulating firebrick (IFB; not shown in FIGS. 1A and 1B). Conventional tunnelcross-sections with bricks that are 6 in wide, tunnel walls that are 96in tall, and a solid lid that is 9 in thick results in a load on thesupporting IFB layer of 11.6 psi. Published data using ASTM testingshows that at the temperatures present in the reformer furnaces, thebase IFB layer will deform a full 1% under those loads in 100 hours. Thedeformation of the base IFB layer translates in one of two ways: eitherthe deformation will prematurely compress the fiber allowances forthermal expansion, or the deformation will reduce the overall insulatingvalue of the base IFB. Both instances are known to result in failure.

The effects of temperature and tunnel mass are not limited to theinternals of the furnace, but can also cause deformation of thesupporting furnace structure, leading to a non-uniform furnace floor.Conventional tunnel designs utilize mortared joints to secure the bricksto one another, effectively turning the large number of small bricksinto a small number of large wall sections. These wall sections act as asingle body, and cannot accommodate any major dimensional change in thefurnace floor. Deformation of the supporting furnace structure willtherefore result in the failure of a conventional tunnel.

Differential thermal expansion occurs not only in situations withdifferent design materials, but also across large sections of materialsthat are expected to act as a single body. Conventional tunnel designalso uses fiber expansion joints roughly every 6-10 feet of wall length,with all of the building components in between adhered to one anotherwith a refractory mortar. This refractory mortar also causes the wallsections to behave as a single body. No furnace has a completely uniformtemperature distribution, however, and at some point, differentialthermal expansion will occur across a wall section. The stressesimparted on the wall section are the same as those that cause thermalshock within a singularly body.

FEA has been performed to determine stress levels associated with adifferential temperature from the top of a fully mortared 10 ft wallsection to the bottom, where the fully mortared wall section was treatedas a single body for the purposes of the analysis. The bottom of thewall section was 1925° F. and the top of the wall section was 1900° F.,with a uniform temperature distribution in between. The FEA alsoincluded a simulated weight of the tunnel lids and gravity, but no otherexternal forces. It was shown that the stress of the system exceeds the500 psi HMOR of a standard refractory mortar. Since the mortar jointsare the weakest point on the wall, they crack to alleviate the stress.The more cracking that occurs in the mortared wall, the smaller the wallsections become, and the lower the stresses become in any one section.

Properly accommodating for thermal expansion is one of the mostdifficult aspects of any thermal application design. Conventional tunneldesigns use a different materials and designs for the tunnel lid and thetunnel base. Many tunnels have low density refractory or fiberinsulation in the “base” area in between the wall supporting IFBcolumns. The tunnel lid can expand as much as ⅜ in, thereby pushing thetunnel walls apart, whereas the fiber insulation will not impart anyexpansion forces on the tunnel walls. The resulting trapezoidal shape issusceptible to buckling and collapsing. In certain situations, tunnelshave been found at the conclusion of a furnace campaign to havealternative movement in the lateral direction. This is more commonlyknown as “snaking,” and is the result of the overall tunnel attemptingto expand greater than the built-in allowance. This movement will crackthe mortar, separate the walls from lids, and push the walls off of theIFB base; all of which lead to failure. While traditional tongue andgroove brick design with a circular cross section (see, e.g., FIGS. 4and 5) is somewhat effective in preventing lateral movement, thisarrangement does will not sufficiently arrest buckling, as the rotationof one block relative to the block below it will separate the tonguefrom the groove, allowing a full system collapse (see, e.g., FIG. 15).

In addition to the above problems with the traditional wall design andcomponents themselves, installing a conventional tunnel system requiresa number of skilled labor positions that are becoming increasinglychallenging to fill, particularly for temporary needs. This oftencreates a situation where the proper level of skilled labor is notavailable, and the overall quality of resultant installed tunnel systemis compromised or the installation costs become higher than expected. Insome instances, a conventional tunnel system has simply operated for thefull amount of its originally projected life span, but due to short timeframe of a turnaround schedule the tunnel cannot be fully repaired orreplaced and must continue to perform for an extended campaign. Thelength of time and the high skill level required to install aconventional tunnel system therefore becomes a cause for the reliabilityissues. The full extent of damage that may be imparted to a tunnelsystem is often unknown prior to a turnaround, so a maintenanceengineering crew has only a few weeks to examine, design, and implementrepairs that are meant only to keep the tunnel system operational untilthe next turnaround, where this kind of repair can be attempted again.This is can be a very dangerous gamble for a plant, based on the longlead time and installation time associated with replacing the tunnelswhen a failure results in an unplanned outage.

The extended time frame and high level of skill required forinstallation and repairs imparts undesirable variability in qualityoutput for conventional tunnel systems. Repairs that end up takinglonger than the available window of plant turnaround time are not aviable option, and often result in an undesirably extended tunnelcampaign. There is a strong desire to reduce the overall installationtime and need for highly skilled labor in order to decrease thisvariability in quality. In some cases, conventional tunnel systemsrequire overhead cranes to be installed to assist in the handling of theheavy tunnel lids.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a light-weight,free-standing tunnel structure, without the use of mortar, that betterwithstands the application of hydrogen reformers, using moremechanically robust refractory components that are made of higherperformance material. More specifically, it is an object to the presentinvention to overcome the drawbacks of the prior art by providinglight-weight, structurally stable parts, implementing system designsthat avoid putting individual components into tension, and using designswith a network of evenly distributed, highly engineered expansion gapsthat ensure the correct amount of room for thermal growth, but which donot require any precision measurement at installation.

According to the present invention, a refractory tunnel assembly for asteam reformer furnace is provided. The tunnel assembly comprises aplurality of hollow base components, each base component comprising aplurality of corresponding mechanical mating members, a plurality ofhollow wall blocks, each wall block comprising a plurality ofcorresponding mechanical mating members that further correspond to themechanical mating members of the base components, and a plurality ofhollow lid components, each lid component comprising a plurality ofmechanical mating members that further correspond to the mechanicalmating members of the base components and the wall blocks. The basecomponents are arranged to extend in a horizontal arrangement direction(first direction) defining a width of the tunnel assembly and in alongitudinal arrangement direction defining a length of the tunnelassembly. The wall blocks are stacked upon and mechanicallyinterconnected to the base components via the corresponding mechanicalmating members, without the use of mortar, in a vertical arrangementdirection (second direction) and along the longitudinal arrangementdirection, and are stacked upon and mechanically interconnected to oneanother via the corresponding mechanical mating members, without the useof mortar, in both the vertical and longitudinal arrangement directions,to define two parallel tunnel walls, spaced a distance apart from oneanother in the horizontal arrangement direction (defining an internalwidth of the tunnel), that extend upwardly from the base components inthe vertical arrangement direction and extend along the length of thetunnel assembly (in the longitudinal arrangement direction) on the basecomponents. The plurality of lid components are stacked upon andmechanically interconnected to the wall blocks via the mechanical matingmembers, without the use of mortar, in the vertical arrangementdirection and along the longitudinal arrangement direction, so that thelids extend along the longitudinal arrangement direction and acrosshorizontal arrangement direction in order to cover the distance betweenthe two tunnel walls in the horizontal arrangement direction along atleast a portion of the length of the tunnel assembly.

Preferably, the base components, the wall blocks and the lid componentsall comprise the same material.

According to one aspect, the plurality of mechanical mating memberscomprise at least one pair of male and female components provided incorresponding locations on upper and lower surfaces of each of the basecomponents, the wall blocks and the lid components.

Preferably, the male components comprise a protruded portion extendingfrom the upper surfaces of each of each of the base components, the wallblocks and the lid components, and the female components comprise acorresponding opening in the lower surfaces of the each of the basecomponents, the wall blocks and the lid components.

According to another aspect, the at least one pair of corresponding maleand female components comprises two pairs of male and female componentsprovided in corresponding locations on upper and lower surfaces of eachof the base components, the wall blocks and the lid components.

It is also preferred that at least a portion of the plurality of thewall blocks further comprises at least one through-hole formed inopposed side surfaces thereof, the though-hole being in communicationwith the tunnel but not being in communication with an inner cavity ofthe hollow wall blocks.

Preferably, at least a portion of the plurality of wall blocks furthercomprise a tie bar cradle formed in a side surface thereof proximate anupper surface thereof, and that the refractory tunnel assembly furthercomprises at least one tie bar extending between the tunnel walls in thehorizontal arrangement direction.

According to another aspect of the present invention, a refractory blockfor a steam reformer furnace tunnel is provided, the refractory blockcomprising a hollow main body portion having an outer peripheral surfacedefining a first end, an opposed second end, an upper surface, anopposed lower surface, a first side and an opposed second side. At leastone first mechanical mating member defining a protruded portion isprovided, extending from a portion of the upper surface of the main bodyportion, at least one second corresponding mechanical mating memberdefining an opening corresponding to the protruded portion is formed ina portion of the lower surface of the main body portion, at least onethird mechanical mating member defining a tab is provided in a portionone of the first end and the opposed second end or the first side andthe opposed second side of the main body portion, at least one fourthmechanical mating member comprising a groove corresponding to the tab isformed in the other of the first end and the second end or the firstside and the opposed second side of the main body portion, and at leastone cavity is formed in the lower surface of the main body portion ofthe refractory block.

Preferably, a wall thickness of the refractory block is in a range of0.65 to 0.875 in.

It is preferred that the at least one first mechanical mating membercomprises two first mechanical mating members, and the at least onesecond corresponding mechanical mating member comprises two secondcorresponding mating members.

According to one aspect of the present invention, the block comprises abase component for a tunnel assembly, and the at least one thirdmechanical mating member comprises two tabs provided in horizontallyopposed portions of one of the first side and the opposed second side ofthe main body portion, and the at least one fourth mechanical matingmember comprises two grooves formed in corresponding positions on theother of the first side and the opposed second side of the main bodyportion.

According to another aspect of the present invention, the blockcomprises a lid component for a tunnel assembly, and the at least onethird mechanical mating member comprises two tabs provided inhorizontally opposed portions of one of the first side and the opposedsecond side of the main body portion, and the at least one fourthmechanical mating member comprises two grooves formed in correspondingpositions on the other of the first side and the opposed second side ofthe main body portion.

According to another aspect of the preset invention, the refractoryblock comprises a wall block for a tunnel assembly, and the tab of thethird mechanical mating member is provided in a portion of one of thefirst end and the opposed second end of the main body portion, and thegroove (of the fourth mechanical mating member) corresponding to the tabis formed in the other of the first end and the second end of the mainbody portion. It is also preferred that the wall block further comprisesat least one through-hole having opposed openings formed in the firstside and the opposed second side of the block, and which is not incommunication with the at least one cavity of the main body portion ofthe refractory block.

Thermal stresses associated with a temperature differential across abody can result in failure from thermal shock. There are a number ofapproaches that are utilized to reduce the thermal stresses below theyield strength of a refractory component. Decreasing the wall thicknessof the refractory component allows for the thermal conductivity of thematerial to equalize the wall temperature and eliminates the stressesassociated with the thermal differential. The wall thickness should beas thin as possible without sacrificing the overall stability of thetunnel system. Since the tunnel system is only self-supporting, reducingthe wall thickness of all of the components also decreases the overallsystem weight.

Providing the optimal wall thickness is achieved by the proper balanceof strength and weight. Thinner walls reduce thermal stresses and systemweight, but thicker walls can support more load. In view of the above,the wall thickness is preferably in a range of about 0.5 in-1.5 in, mostpreferably in a range of 0.625 in to 0.875 in. The desired weight foreach component is specified herein, and is about 40 lbs-60 lb for theblocks, 50 lb-75 lb for the lids, and 70 lb-150 lb for the bases.

In addition to reducing the wall thickness of the individual components,the “sections” of the tunnel system are reduced so that the differentialtemperature seen by a single section is minimized. Ideally the“sections” of the tunnel system should only be as large as theindividual building components. In order to accomplished this, everyblock must manage its own thermal expansion, and the entire system mustbe mortar-free, but for stability maintenance, must be completelyinterconnected. This is accomplished by providing precision formed,robustly mechanically inter-connectable refractory components, and aninstallation procedure that automatically accommodates for thevariability in each component.

In order to ensure proper thermal expansion management, the tunnelsystem also utilizes a base component that is made of the same materialand has substantially similar dimensions with respect to the lid (cover)component. This ensures that the tunnel expands and contracts equally onboth the top and bottom of the wall, maintaining the overall structureand reducing stresses that could otherwise cause buckling. Buckling canalso be arrested by virtue of the robust and tight toleranceinterlocking mechanical mating feature provided in the wall components,so that the rotation of a block in relative to a block below it does notbreak direct contact.

Even if the thermal expansion is properly managed, in order to furtherprevent buckling from still being an issue as a result of delayedignition or a non-uniform furnace floor, cross-beams or tie bar (tierod) supports are also provided at predetermined locations.

Proper material selection and installation procedures are also importantto prevent “snaking.” Many materials will increase in overall dimensionwhen re-heated, increasing variability and adding challenge to thethermal expansion management. Because the coefficient of thermalexpansion for refractory components is nonlinear, it must be fullycharacterized and understood to ensure that proper expansion joints arecreated. Selecting a suitable material has always been about compromiseand sacrifice in connection with conventional tunnel designs. That is,conventionally, bricks that have sufficient insulating value to keep thefurnace supports from deforming do not always also have enough strengthto adequately support the tunnel system, and bricks with higherstrengths do not have the required insulating value. Conventionalmaterials include various types of fire bricks and super duty brick.

The coefficient of thermal expansion (CTE) for the selected materialshould not simply be assumed as a linear function for the materials usedin the tunnel system. Having a fully characterized CTE is preferable forensuring that the expansion behavior is properly managed. This becomeseven more critical when the thermal expansion is managed on a singlecomponent level. Proper material selection preferably includesconfirming that the modulus of rupture at the service and excursiontemperatures of the furnace has a sufficient safety factor when comparedto the associated static load stresses. Selecting a material with animproved HMOR provides immediate increases to the safety factor in thesystem. Knowing the room temperature MOR of a refractory material aloneis not sufficient for proper design of a tunnel system.

In addition, any material being selected for use in a reformer furnaceshould preferably have the highest resistance to creep reasonablyavailable, as a reduced creep will prolong the life of the tunnel systemand prevent premature failures. The use of a material with improvedcreep resistance reduces the tension on the bottom side of the top lids,and reduces the outward force that the top lids exert onto the brickwalls of the tunnel, which is preferred. Using a material having a fullycharacterized CTE, higher HMOR, and increased creep resistance togetherimproves the overall reliability of the tunnel system.

In view of the above, in the present invention, suitable materials forthe bricks (blocks), bases and the covers (lids) include, but are notlimited to alumina-based refractory materials, cordierite (magnesiumaluminum silicate), and zirconia, for example. More preferably, theblocks, lids and bases are made from a material selected from the groupconsisting of medium duty fire clay brick (Oxide Bonded Aluminacomprised of at least 30% alumina by weight), high duty fire clay brick(Oxide Bonded Alumina comprised of at least 35% alumina by weight),super duty fire clay brick (Oxide Bonded Alumina comprised of at least40% alumina by weight), and high alumina fire clay brick (Oxide BondedAlumina comprised of at least 60% alumina by weight). Most preferably,the present invention utilizes Mullite Bonded Alumina comprised of 88%alumina by weight or an Oxide Bonded Alumina comprised of 95% alumina byweight.

The tunnel according to the present invention also utilizes a basecomponent that distributes the weight load of the wall over an area thatis roughly 5 times larger than the conventional design. The light-weightdesign of the present invention, coupled with the inventive basecomponent, typically results in a load on the base layer of 1.4 psi.This allows for the use of highly insulating materials, which improvesthe overall reliability of the structural furnace supports and thereforthe overall system.

As mentioned before, a conventional tunnel cross-section, with bricksthat are 6 in in width, tunnel walls that are 96 in tall, and a solidlid that is 9 in thick, results in a load on the supporting IFB layer of11.6 psi and a deformation of 1% within the first 100 hours of thecampaign. Decreasing the overall weight of the entire tunnel system by60% translates into a significantly lower PSI load, and results in anorder of magnitude less deformation to the base layer, thus increasingthe effective production life and efficiency of the tunnel.

With the reduced wall thickness and improved materials providedaccording to the present invention, the light-weight tunnel lids can beeasily installed or removed by two laborers. In addition, thelight-weight, mortar-free block design with interlocking components iseasily handled by one laborer, and the tunnel structure can assembled,repaired and/or disassembled as necessary without significantconsequence or the requirement for high levels of skill. Cross beamsupports (i.e., tie bars) can be easily added or removed withoutlimiting access to other tunnel components during turnarounds, ensuringthat repairs can be complete and effective. Faster installation andrepair time also allows for proper repairs to be made more readily,improving the overall reliability of the system.

Reducing the weight of the components, while maintaining the structuralintegrity of the building blocks, makes it possible to eliminate much ofthe crushing force on the lower courses of the brick. Providinglight-weight, structurally correct cover (lid) segments overcomes thedrawbacks previously associated with making those components thicker inorder to be stronger, which also detrimentally added additional load tothe entire system. The incorporation of expansion gaps between eachbrick and elimination of mortar from the system ensures that theassembly can expand and contract without the creation of largecumulative stress, and reduces the installation time of the tunnel as awhole.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and object of the presentinvention, reference should be made to the following detaileddescription of a preferred mode of practicing the invention, read inconnection with the accompanying drawings, in which:

FIG. 1A is a perspective cut-view of a conventional hydrogen reformerfurnace, and FIG. 1B is a sectional end view of the furnace shown inFIG. 1A;

FIG. 2 is a perspective view of a conventional tunnel assembly used inthe furnace shown in FIGS. 1A and 1B;

FIG. 3 is a perspective view of a conventional solid lid;

FIG. 4 is a perspective view of a conventional single tongue and grovetype block (brick);

FIG. 5 is a perspective view of a conventional double tongue and grovetype block (brick);

FIG. 6 is an end view of a conventional hollow lid;

FIG. 7 is a perspective view of the conventional hollow lid shown inFIG. 6;

FIG. 8 is a perspective view of a conventional off-set lid;

FIG. 9 is a perspective view of a conventional tongue and groove lid;

FIG. 10 is a perspective top view of a half block (brick) according toone aspect of the present invention;

FIG. 11 is a perspective top view of a full block (brick) according toone aspect of the present invention;

FIG. 12 is a perspective bottom view of the full block shown in FIG. 11;

FIG. 13 is a sectional end view of two blocks shown in FIG. 11 in astacked arrangement;

FIG. 14 is a sectional end view of the stacked arrangement shown in FIG.13 under rotational force to illustrate that the stacked blocks to notdisengage;

FIG. 15 is an end view of prior art blocks shown in FIG. 4 underrotational force to illustrate that those blocks do disengage under thesame type of rotational force;

FIGS. 16A and 16B are perspective top and bottom views of a full blockincluding a though-hole;

FIG. 17 is a perspective view of a full block having two through-holes;

FIGS. 18A and 18B are perspective top and bottom views of a horizontalinterlocking full block according to another aspect of the presentinvention;

FIG. 19 is an end view of the block shown in FIG. 18;

FIG. 20 is a perspective view of a partial assembly stack of blocksshown in FIG. 18;

FIG. 21 is a perspective top view of a full width base componentaccording to the present invention;

FIG. 22 is a perspective bottom view of the full width base componentshown in FIG. 21;

FIG. 23 is a perspective top view of a single side base componentaccording to another aspect of the present invention;

FIG. 24 is a bottom perspective view of the single side base componentshown in FIG. 23;

FIG. 25 is a perspective view of the full block shown in FIG. 16,further provided with a tie bar cradle;

FIG. 26 is a perspective view of a tie bar;

FIG. 27 is a perspective view of two full blocks according to FIG. 25and a tie rod according to FIG. 26 situated in the respective tie barcradles and spanning the horizontal distance therebetween;

FIG. 28 is a perspective view of two full blocks and another tie baraccording to a different aspect of the present invention;

FIG. 29 is a perspective top view of a lid according to the presentinvention;

FIG. 30 is a perspective bottom view of the lid shown in FIG. 29;

FIG. 31 is a perspective view of a tunnel assembly according to thepresent invention;

FIG. 32 is a side view of the tunnel assembly shown in FIG. 31;

FIG. 33 is an end view of the tunnel assembly shown in FIGS. 31 and 32;and

FIG. 34 is a perspective view of the assembly shown in FIG. 31 with somewall blocks removed to show the location of the tie bars.

DETAILED DESCRIPTION OF THE INVENTION Blocks (Also Referred to HereinInterchangeably as Bricks)

The flue gas tunnel according to the present invention comprises aplurality of refractory blocks or bricks that are engineered withprecision interlocking mechanical mating features to facilitate stackinginterconnection to form the free-standing tunnel walls without the useof mortar. These mechanical mating features are also specificallydesigned to allow for thermal expansion in service while simultaneouslypreventing the wall from becoming disassembled prematurely.

One example of a mating feature has a geometry that requires horizontalinstallation and prevents the block from becoming disassembledvertically. FIG. 10 shows a “half brick” 1 and FIG. 11 shows a “fullbrick” 10 according to this aspect of the present invention. FIG. 12 isa bottom view of the full brick 10 shown in FIG. 11. It should beunderstood that the corresponding bottom view of the half brick 1 shownin FIG. 10 (not shown) would be same as that shown in FIG. 12, only halfthe size. A standard brick has dimensions of, for example, 6.5 in W×18in L×10 in T (tall), but the design is applicable for bricks as small as2 in W×4 in L×2 in T and for bricks as large as 9 in W×24 in L×18 in T,as well. Preferably, each block (brick) has a weight in a range of 20-70lb, more preferably 40-50 lb, so that one person can readily maneuverthe blocks alone, while reducing the total number of blocks needed toconstruct the tunnel wall to the smallest number possible.

Each of the bricks 1, 10 has an outer peripheral surface defining afirst end (1 a, 10 a), an opposed second end (1 b, 10 b), an uppersurface (1 c, 10 c) and an opposed lower (bottom) surface (1 d, 10 d).These bricks 1, 10 are hollowed out to remove all possible material fromnon-critical areas. Preferably, the wall thickness “t” (see, e.g., FIG.12) walls of these bricks 1, 10 is in a range of 0.5-1.5 in, preferably0.625-0.875 in. The resultant tunnel assembly has only about 60% of theweight of a conventional tunnel. The hollowed-out portions define one ormore, preferably a plurality of cavities 2 in the respective blocks 1,10.

The upper surfaces 1 c, 10 c of the blocks 1, 10 each include a malepart of the precision interlocking mechanical mating features of therefractory blocks according to the present invention. The protrudingportion 3 is elevated a distance from the surface 1 c, 10 c to define ageometrical member that extends from the block 1, 10 and serves as alocking part that fits precisely into the opening 4 formed in the lowersurface 1 d, 10 d of the blocks 1, 10. As shown, the protruding portion3 is a substantially rectangular elevation with chamfered corners and acircular opening 3 a passing through its center and in communicationwith a cavity 2. The circular opening 3 a is merely a function ofmanufacturing and material removal considerations, and is not critical.As shown in FIGS. 10 and 11, the openings 3 a are in communication withthe cavities 2. This is not always the case, however, as described inmore detail below.

While the exact shape of the protruding portion 3 is not necessarilylimited to the shape shown here, it is preferably a geometric match tothe shape of the corresponding opening 4, with a slight off-set toaccommodate manufacturing tolerances. The protruding portions 3 of theblocks 1, 10 must fit precisely within the openings 4 of the verticallyadjacent blocks 1, 10 to securely engage the vertically adjacent blocks1, 10 to one another to facilitate the construction of free-standingtunnel walls without the use of mortar. There must also be sufficienttolerance to account for the thermal expansion considerations discussedabove, and to maintain contact to prevent buckling.

The opening 4 communicates with the cavities 2 of the blocks 1, 10, andreceives the protruding portion 3 in a tight, interlocking manner tosecurely connect the blocks 1, 10 to one another, without mortar, in avertically stacked manner, as shown in FIG. 13. The shape of the opening4 is not critical, so long as it precisely corresponds in shape and sizeto the shape and size of the protruding portions 3, in consideration ofthe mechanical factors and thermal concerns discussed above.

The importance is the geometric match with a slight off-set between thecorresponding protruding portion 3 and opening 4 into which theprotruding portion 3 fits. Preferably, the off-set is in a range of0.020 in to 0.060 in. The minimum off-set is dictated by manufacturingtolerance capabilities resulting in block to block variability. Theremust be sufficient height and tightness to securely engage if bucklingoccurs. Preferably, the overall height “h” of the protruding portion 3,or distance that the protruding portion 3 extends from the upper surface1 c, 10 c of the blocks 1, 10, is at least 0.75 in, in order to ensuresufficient engagement with the opening 4 and prevent buckling. Thedimensions of the opening 4 should be as tight to the protruding portionas possible with allowance for manufacturing variation. Ideally, uniformwall thickness balanced with manufacturing needs governs the dimensions.

The individual blocks 1, 10 further include additional mechanical matingfeatures, such as a tab on one end and a groove on the other end, with agap provided that allows each block to expand with increasing operatingtemperature until its seals against the blocks on either side thereof inthe horizontal arrangement direction. As shown in FIGS. 10-12, the firstsides 1 a, 10 a of the blocks 1, 10 include a groove or slot 5, and theopposed second sides 1 b, 10 b are formed to include a corresponding“tab” or protrusion 6 that vertically fits into the corresponding groove5 of a horizontally adjacent block 1, 10. Preferably, the groove islarger than the tab by a minimum of manufacturing variation; preferably,the tab is 30-75% of the overall width of the block.

A compressible high temperature insulation fiber (not shown) can also beprovided, placed in the groove 5 in order to reduce gas bypass whileaccommodating for a range of temperature fluctuations in service. Thefiber is specified to have sufficient compression variability so as toreduce gas bypass over a wide range of operating temperatures from 600°C.-1200° C. This fiber can also be used in between layers of blocks toprevent point loading. As discussed below, the base components and toplids (covers) both have a similar tab and groove design, and use eithera fiber gasket or a fiber braid to reduce gas bypass over the range ofoperating temperatures.

Preferably, as the blocks 1, 10 are arranged in the formation of thetunnel wall, the blocks 1, 10 are horizontally off-set by one-half of ablock length, or by one set of mechanical mating features, to increasethe mechanical robustness of the arrangement (see, e.g., FIG. 34). Thisarrangement also helps prevent buckling, which is arrested by virtue ofthe robust and tight tolerance interlocking mechanical mating feature,so that the rotation of one block relative to a block below it does notcause direct contact between the respective protruding portion 3 and theopening 4 to break, as shown in FIG. 14. On the other hand, FIG. 15shows how rotational forces on prior art tongue and groove blocks (seeFIG. 4) can cause separation between the blocks, and direct contactbetween the respective tongue and groove features significantly breaks,which leads to wall collapse.

In order for the tunnel to properly act as a flue for the exit of thefurnace, it must have variable inlet conditions (openings in the walls)that allow more gas to enter the tunnel farthest from the exit, and lessgas to enter the tunnel closer to the exit. This creates a more uniformdistribution of gas and temperature in the furnace. As noted above,conventional tunnel wall designs simply utilize half bricks to creategaps in the walls as various locations. However, such conventional halfbricks create unsupported locations on top of the square openings,creating locations for failures. As shown in FIGS. 16-17, the tunnelsystem according to the present invention utilizes refractory blocks100, 101 that include one or more through-holes 7 that are formedtherein in order to allow gas to enter the tunnel. This design evenlydistributes the load created by the through-holes 7 to the surroundingmaterial. The through-holes 7 can be formed when the bricks 100, 101 areinitially formed (e.g., cast), or can be formed later by machining orany suitable process.

The through-holes 7 can have any geometry, but preferably have asemi-circular shape. The size of the through-holes 7 can vary from 1 in²up to substantially to the full size of the block 100, 101, which istypically around 144 in², but are preferably 12 in²-36 in². Blocks 100,101 preferably have one or two through-holes 7 per block, but could havemultiple holes in various locations to facilitate the same end result,as desired. These through-holes 7 can be closed, i.e., do notcommunicate with the interconnected internal cavities 2 of the blocks100, 101 that form an internal area of the tunnel wall, as shown, orinstead, a small number of blocks could have through-holes that are opento the internal area of the tunnel wall.

As shown in FIGS. 16A and 16B, the opening 3 b in the protruding portion3 is simply a removed-material portion, and does not communicate with(not in fluid communication with) the cavity 2. The through-hole 7 islike a tube that passes though the cavity 2, but the internal surface 7a of the through-hole 7 is not in fluid communication therewith, and thethrough-hole 7 (though which the gasses pass) is therefore closed to thecavities 2 (and therefore the internal surface area of the tunnel wall)by virtue of the external surface 7 b of the through-hole 7. FIG. 17shows a block 101 with two through-holes 7, but in that case, that theprotruding portions 3 do not include any material-removed portions. Theprotruding portions 3 instead have a solid geometry to prevent gas beingintroduced into the tunnel from going into the wall cavity space (i.e.,the internal surface area of the tunnel wall).

FIGS. 18-20 show an example of a refractory block 20 according toanother aspect of the present invention having a different type ofmechanical mating feature that requires vertical installation and whichprevents the blocks 20 from becoming disassembled horizontally. Each ofthe bricks 20 has an outer peripheral surface defining a first end 20 a,an opposed second end 20 b, an upper surface 20 c, and an opposed lower(bottom) surface 20 d.

The upper surface 20 c of each block 20 includes a plurality male partsof the precision interlocking mechanical mating feature according to thepresent invention. The protruding portions 23 are elevated from thesurface 20 c to define a geometrical member that serves as a lockingpart that fits precisely into the opening (slot) 24 formed in the lowersurface 20 d of the blocks 20 when slidably introduced horizontally. Asshown, an end surface of the protruding portions 23 are formed flushwith the first end 20 a of the block 20 (end surface) and the second end20 b of the block 20 (end surface). As shown in FIG. 18B, the blocks 20are hollow, and include a plurality (e.g., two) of cavities 2. If theblocks 20 were to include a through-hole 7 (not shown), the cavitieswould be formed shallower, and the though-holes would be formed to passtherethough without communicating therewith in most cases. The wallthickness “t” of the block 20 is the same as that described above.

The protruding portions 23 are substantially rectangular elevations ortruncated rectangular elevations in shape with chamfered corners. Whilethe exact shape of the protruding portion 23 is not limited to theshapes shown here, any cross-sectional shape where the top dimension isgreater than the bottom dimension, such as a modified invertedtrapezoidal shape. The protruding portions 23 of the blocks 20 musthorizontally fit (slide) precisely within the opening (slot) 24 of thevertically adjacent blocks to securely engage the vertically adjacentblocks to one another to facilitate the construction of a free-standingtunnel walls without the use of mortar. The tolerances must besufficient to ensure secure mechanical engagement while accounting forthermal expansion considerations and manufacturing variability, asdiscussed above.

A shown in FIG. 18B, the opening 24 is formed in the block walls alongsubstantially extends along the entire length of the block 20 from thefirst end 20 a to the second end 20 b and slidably receives theprotruding portions 23 in a tight, interlocking manner to securelyconnect the blocks 20 to one another in a vertically stacked manner, asshown in FIG. 20. The protruding portions 23 each also include a lip 23a that engages a ridge 24 a along the opening 24 to further preventvertical disengagement of the stacked blocks 20. The shape of theopening 24 is not critical, so long as it precisely corresponds in shapeand size to the shape and size of the protruding portions 23. As shown,D1>D2>D3.

As shown in FIG. 20, the installation of these blocks 20 are alsopreferably staggered at a half-width distance, without the use ofmortar, so that a single block 20 engages two blocks 20 in the row aboveit, and two blocks 20 in the row below it (e.g., off-set by one matingfeature engagement, as discussed above). This style of mechanical matingalso controls the expansion of the blocks 20 by limiting how far anyindividual part can shift from its original position relative to theblocks 20 around it.

Both of the mechanical mating features described above add redundancy tothe system by mechanically engaging the blocks, which prevents thetunnel wall from leaning and falling over without requiring that matingfeatures be sheared off or otherwise break through the wall of the blockto which they are connected.

Base Component

Another feature of the tunnel according to present invention is the basecomponent 30, shown in FIGS. 21 and 22. A plurality of base components30 run the length of the tunnel and span the horizontal width ‘w’ of thetunnel to connect the two walls together using the same mating featuresas the wall blocks 10, 100 described above (see, e.g., FIGS. 33 and 34).

Each base component 30 has an outer peripheral surface with an uppersurface 30 c and an opposed lower (bottom) surface 30 d on which theinterlocking mechanical mating features 33, 34 are formed. Theprotruding portions 33 correspond to the protruding portions 3 describedabove in connection with the bocks 1, 10, 100 and the openings 34correspond to the openings 4 described above in connection with theblocks 1, 10, 100. The same critical dimensional requirements for themechanical mating members and wall thicknesses discussed above apply tothe base components, as well. Preferably, each base component 30 has atotal weight in a range of about 75-150 lb, more preferably about 100lbs.

The protruding portions 33 are provided on the upper surface 30 a of thebase components 30 proximate the two opposed ends 30 a, 30 b, so as tocorrespond to the laterally (horizontally) opposed locations of thetunnel walls to be built thereon. The openings 34 are provided in thebottom surface 30 d of the base component 30 in corresponding locations,as shown in FIG. 22. The base component 30 has a plurality of cavities32 from which unnecessary material has been removed to reduce the weightof the base block. As shown, the openings 4 communicate with suchcavities 32, and a plurality of additional cavities 32 are providedalong the length of the base component 30, separated by interior blockwalls having sufficient thickness “t” to provide enough material toensure the structural integrity of the component is maintained. The wallthickness is preferably in a range of 0.5 to 1.5 in, preferably 0.625 to0.875 in. The base components 30 also have additional mechanicalmating/expansion features such as the grooves 35 formed on side surface30 f (see FIG. 22) and protrusion or tab 36 formed on side surface 30 e(see FIG. 21). These features serve the same purpose and function as thefeatures 5 and 6 described above in connection with the blocks 1, 10.The position of these mechanical/expansion features 35, 36 correspondsto the mating alignment with the other base components 30 and the wallblocks to be stacked thereon, as described below in more detail inconnection with FIGS. 31-34.

As noted above, it is important that the size and material of the basecomponent 30 is substantially the same as that of the lid (discussed inmore detail below) in order to properly and effectively compensate forthermal and stress factors, although the base is a heavier component, asone skilled in the art can appreciate.

An example of another base component 40 is shown in FIGS. 23 and 24.This base component is referred to as a single side base, and isessentially a standard wall block 10 (see, e.g., FIG. 11) having anenlarged bottom cross-sectional area 42 to spread the weight of the wallover up to three times the standard block area. A sectioned, supportedflange 41 can be provided on one or both sides of the base block 40, asshown. The flange structure 41, 42 can be formed as an integral part ofthe block 40 design when the block 40 is cast, can be formed as separatemembers and added later with adhesives and/or co-firing techniques, orcan be machine-formed (tooled) using known techniques. This design wouldbe particularly appropriate in applications where the use of a secondaryprocess would allow other manufacturing processes to make the sameshapes a cast part.

Tie Bars (Also Referred to Herein Interchangeably as Cross BeamSupports)

In the present invention, a tie bar component is used in the assembly atvarious points to secure the walls in place to prevent movement, bothinward and outward, as shown in FIGS. 33 and 34. The tie bar 50 (alsoreferred to as a tie rod or cross beam support) is shown in FIG. 26.This tie bar 50 engages and supports the tunnel walls in various ways,as described below.

FIG. 25 shows one example of a block 100 according to the presentinvention that further includes a tie bar cradle 15 formed thereon,which is a pre-cast saddle (cradle) formed on a top surface 10 c andside surface 10 e of the block 100 facing the inside of the tunnel wall.The tie bar cradle 15 is a semi-cylindrical protrusion having interiorannular rim features to guide, receive and retain the correspondingannular flanges 51 at the ends 50 a, 50 b of the tie bar 50 whenvertically positioned into place therein (see FIG. 27). Refractoryblocks 100 with the cradles 15 formed thereon can be positioned atvarious locations along the tunnel walls when the tunnel walls arebuilt, and then tie bars 50 can be readily added during installation, orlater removed as needed without requiring substantial down time orcreating deleterious maintenance issues.

The tie rods 50 are placed at various points in the system to improvethe overall stability of the tunnels in service, as one skilled in theart can readily determine. The tie rods 52 can engage a single point oneither side of the wall, as shown in FIG. 27, or multiple points. Forexample, instead of a single beam-shaped tie bar 50, an H-shaped tie bar(not shown) could be used to instead engage multiple points (2 points oneach side) of the opposed tunnel walls at the same time. The span of thetie bar 50 is substantially the same as the span of the top lid and thebase component, which can be as small as 12 in or as wide as 60 in,although the preferred size is a range of 24 in to 36 in (correspondingto the internal width of the tunnel). It is understood that the lengthof the tie bars is governed strictly by the designed width of thetunnel, with clearance to allow for thermal growth. The cross-sectionaldiameter of the tie bar 50 is preferably 1-8 in, more preferably 3-4 in.

FIG. 28 shows another method of positioning tie bars 52 in the tunnelwall as it is initially constructed. In this case, however, a quartercircle of area in a corresponding portion 10 g on each block 102 isremoved proximate the upper surface 10 c to provide for a locationsufficient to accommodate the positioning of a tie rod 52 in a capturearea between the flanges 51 and 53 thereof.

Lids (Also Referred to Herein Interchangeably as Covers)

In the present invention, the span of the top lid 60 can be as small as12 in, or as wide as 60 in, although the preferred size is a range of 24in to 36 in. Preferably, each lid component has a total weight in arange of 50-125 lb, more preferably in a range of 60-80 lbs.

As shown in FIG. 29, the upper surface 60 c of lid 60 has a flat topwith angled sides. The upper surface 60 c of the lid also includes thesame interlocking mechanical mating features 63 as described above inconnection with the blocks 1, 10 and the base components 30. In the caseof the lid 60, the protruded portions 63 serve two functions. First, theprotruded portions 63 provide mechanical mating features in connectionwith the corresponding openings 4 on other wall blocks 10, 100 in thesame manner discussed above, which enable the lid 60 to be used in anassembly where the lid 60 is not the topmost component, but whereadditional tunnel wall blocks 10, 100 are instead placed on top of thelid 60, and the walls are continued vertically upward. Second, since theprotruded portions 63 extend a distance of at least 0.5 in above (in thevertical direction) the overall surface geometry of the lid 60, thisallows for the placement of a plywood board on top of the lid 60 todefine a walkway during furnace turnarounds. Because this existsdirectly above the tunnel walls, the walkway allows workers access intothe furnace on top of the tunnels without putting weight onto the centerof the unsupported span of the lids, and instead directs all of theirweight onto the tunnel walls, where it can be readily supported.

The lid 60 is also hollowed out from the bottom surface 60 d to removeall possible material from non-critical areas, in order to minimize thestress by improving the ratio of force per unit area of the crosssection. As shown in FIG. 30, a large central cavity 62 is formedthereby, as well as two smaller cavities 62 in communication with theopenings 64 defining the mechanical mating features. The mechanicalmating feature (opening) 64 provides engagement with the protrudedportions 3 of the blocks 10, 100 forming the walls 8 to securely attachthe lid 60 to the walls 8 on either side, spanning the internal tunnelwidth between wall structure. The critical dimensions of the mechanicalmating features are the same as discussed above. Preferably, the wallthickness “t” of the lids is in a range of 0.5 to 1.5 in, morepreferably 0.625 to 0.875 in.

The lids 60 also have additional mechanical mating features such as thegrooves 65 formed on side surface 30 f (see FIG. 30) and protrusion ortab 66 formed on side surface 60 e (see FIG. 29). These features servethe same purpose and function as the mechanical matingfeatures/expansion gap features 5 and 6 described above in connectionwith the blocks 1, 10, 100 and 35, 36 described above in connection withthe base component 30. The position of these mating/expansion features65, 66 corresponds to the mating alignment with the other lids 60 andthe wall blocks 10, 100 stacked thereunder, as described below in moredetail in connection with FIGS. 31-34. In the present invention, thespan of the lid 60 can be as small as 12 in, or as wide as 60 in,although the preferred size is a range of 24 in to 36 in.

The Tunnel Assembly (Also Referred to Interchangeably Herein as aTunnel)

A plurality of base components 30 are arranged to extend horizontally(in a first direction or the horizontal arrangement direction, i.e.,defining a width of the tunnel) and are aligned with respect to oneanother to define a substantially continuous base surface along thelongitudinal extension direction (length) of the tunnel. The basecomponents 30 are secured to one another via the mechanical matingmembers 35, 36 without any mortar. A plurality of wall-forming blocks 10are vertically stacked onto the base components 30 on both opposedsides, along the longitudinal extension direction of the tunnel, whichhelps further secure the base components 30 in place. The blocks 10 arearranged in a sequentially off-set manner, by one half of a length onthe base components 30, using the respective mechanical mating members33 (protruding portions from the base components 30) and 4 (openings onthe blocks 10) to securely fasten the blocks 10 into place on the basecomponents 30 without the use of mortar. The blocks 10 are also securedto one another via the respective mechanical mating members 5, 6. Aplurality of blocks 100 are then stacked vertically and along thelongitudinal extension direction on the row of blocks 10 in a similar,half-block off-set manner.

Additional blocks 10, 100 are then alternately stacked onto one another,secured to one another vertically and horizontally, without mortar, viathe respective mechanical mating members 3, 4, 5 and 6, continuing in ahalf-block, off-set manner, to define two parallel, vertically orientedtunnel walls 8 that extend both in the second (i.e., verticalarrangement direction) from the base components 30 and in thelongitudinal extension direction of the tunnel. As shown, some of theblocks correspond to the blocks 10 shown in FIG. 11 (withoutthrough-holes 7), and some of the blocks correspond to the blocks 100shown in FIG. 16, which include through-holes 7.

The tunnel walls 8 are spaced a predetermined distance (i.e., 12-60 in,preferably 24 to 36 in) apart from one another in the horizontalarrangement direction, dictated by the horizontal span of the basecomponents 30. Tie bars 50 are inserted into the cradles 15 in desiredlocations, as needed. The tunnel assembly is secured by placing aplurality of lids 60 across the tops of the tunnel walls 8, which aresecured in place onto the uppermost blocks 10 via the mechanical matingfeatures (e.g., openings 64 in the lids and the protruding portions 3 ofthe wall blocks 10), and further secured to one another via themechanical mating members 65, 66 in the lids 60 to construct the tunnel200 (also referred to as a tunnel assembly, see, e.g., FIGS. 31-34).

As discussed above, in the tunnel 200 according to the presentinvention, reducing the weight of all of the components, whilemaintaining the structural integrity of each of the individualcomponents, makes it possible to eliminate much of the crushing force onthe lower courses of the brick (i.e., the base components 30). Providinglight-weight, structurally correct cover (lid) components 60 overcomesthe drawbacks previously associated with making conventional lidsthicker in order to be stronger, which also detrimentally addedadditional load to the entire system. The incorporation of controlledexpansion gaps between each brick and elimination of mortar from theoverall system ensures that the tunnel assembly 200 can expand andcontract without creating large cumulative stresses, and reduces theinstallation time of the tunnel assembly 200 as a whole.

With the reduced wall thickness and improved materials used for thecomponents according to the present invention, the light-weight tunnellids 60 can be easily installed or removed simply by two laborers. Inaddition, the light-weight, mortar-free blocks with interlockingmechanical mating features are easily handled by a single laborer, andthe tunnel structure 200 can assembled, repaired and/or disassembled asnecessary without significant consequences or the requirement for highlevels of skill. Cross beam supports (i.e., tie bars 50) can be easilyadded or removed from the tunnel assembly 200 without limiting access toother tunnel components during turnarounds, ensuring that repairs can becomplete and effective. Faster installation and repair time also allowsfor proper repairs to be made more readily, improving the overallreliability of the system.

While the present invention has been shown and described above withreference to specific examples, it should be understood by those skilledin the art that the present invention is in no way limited to theseexamples, and that variations and modifications can readily be madethereto without departing from the scope and spirit of the presentinvention.

What is claimed is:
 1. A refractory tunnel assembly for a steam reformerfurnace, said tunnel assembly comprising: a plurality of hollow basecomponents, each said base component comprising a plurality ofcorresponding mechanical mating members; a plurality of hollow wallblocks, each said wall block comprising a plurality of correspondingmechanical mating members that further correspond to said mechanicalmating members of said base components; and a plurality of hollow lidcomponents, each said lid component comprising a plurality of mechanicalmating members that further correspond to said mechanical mating membersof said base components and said wall blocks; wherein said basecomponents are arranged to extend in a horizontal arrangement directiondefining a width of said tunnel assembly and a longitudinal arrangementdirection defining a length of the tunnel assembly; wherein said wallblocks are stacked upon and mechanically interconnected to said basecomponents via said corresponding mechanical mating members, without theuse of mortar, in a vertical arrangement direction and along saidlongitudinal arrangement direction, and are stacked upon one andmechanically interconnected to another via said corresponding mechanicalmating members, without the use of mortar, in both said vertical andlongitudinal arrangement directions, to define two parallel tunnelwalls, spaced a distance apart from one another in the horizontalarrangement direction, wherein said tunnel walls extend upwardly fromsaid base components in said vertical arrangement direction and alongthe length of said tunnel assembly on said base components; and whereinsaid plurality of lid components are stacked upon and mechanicallyinterconnected to said wall blocks via said mechanical mating members,without the use of mortar, in the vertical arrangement direction andalong said longitudinal arrangement direction, so that said lids extendalong the longitudinal arrangement direction and the horizontalarrangement direction in order to cover said distance between saidtunnel walls along at least a portion of said length of said tunnelassembly.
 2. The refractory tunnel assembly according to claim 1,wherein said base components, said wall blocks and said lid componentsall comprise the same material.
 3. The refractory tunnel assemblyaccording to claim 1, wherein said plurality of mechanical matingmembers comprise at least one pair of male and female componentsprovided in corresponding locations on upper and lower surfaces of eachof said base components, said wall blocks and said lid components. 4.The refractory tunnel assembly according to claim 3, wherein said malecomponents comprise a protruded portion extending from the uppersurfaces of each of each of said base components, said wall blocks andsaid lid components, and wherein said female components comprise acorresponding opening in the lower surfaces of the each of said basecomponents, said wall blocks and said lid components.
 5. The refractorytunnel assembly according to claim 3, wherein said at least one pair ofcorresponding male and female components comprises two pairs of male andfemale components provided in corresponding locations on upper and lowersurfaces of each of said base components, said wall blocks and said lidcomponents.
 6. The refractory tunnel assembly according to claim 1,wherein at least a portion of said plurality of wall blocks furthercomprise at least one through-hole having openings formed in opposedside surfaces thereof, said though-hole being in communication with saidtunnel but not being in communication with an inner cavity of said wallblocks.
 7. The refractory tunnel assembly according to claim 1, whereinat least a portion of said plurality of blocks further comprise a tiebar cradle formed in a side surface thereof proximate an upper surfacethereof.
 8. The refractory tunnel assembly according to claim 7, furthercomprising at least one tie bar extending between said tunnel walls insaid horizontal extension direction.
 9. The refractory tunnel assemblyaccording to claim 1, wherein a wall thickness of said wall block is ina range of 0.65 to 0.875 in.
 10. The refractory tunnel assemblyaccording to claim 1, wherein a wall thickness of said base componentand said lid component is in a range of 0.65 to 0.875 in.
 11. Arefractory block for a steam reformer furnace tunnel, said refractoryblock comprising: a hollow main body portion having an outer peripheralsurface defining a first end, an opposed second end, an upper surface,an opposed lower surface, a first side and an opposed second side; atleast one first mechanical mating member defining a protruded portionextending from a portion of said upper surface of said main bodyportion; at least one second corresponding mechanical mating memberdefining an opening corresponding to said protruded portion formed in aportion of said lower surface said main body portion; at least one thirdmechanical mating member defining a tab provided in a portion one ofsaid first end and said opposed second end of said main body portion orsaid first side and said opposed second side of said main body portion;at least one fourth mechanical mating member comprising a groovecorresponding to said tab formed in the other of said first end and saidsecond end of said main body portion or said first side and said opposedsecond side of said main body portion; and at least one cavity formed insaid lower surface of said main body portion of said refractory block.12. The refractory block according to claim 11, wherein a wall thicknessof said refractory block is in a range of 0.65 to 0.875 in.
 13. Therefractory block of claim 11, wherein said at least one first mechanicalmating member comprises two first mechanical mating members, and said atleast one second corresponding mechanical mating member comprises twosecond corresponding mating members.
 14. The refractory block of claim13, wherein said block comprises a base component for a tunnel assembly,and said at least one third mechanical mating member comprises two tabsprovided in horizontally opposed portions of one of said first side andsaid opposed second side of said main body portion, and said at leastone fourth mechanical mating member comprises two grooves formed incorresponding positions on the other of said first side and said opposedsecond side of said main body portion.
 15. The refractory blockaccording to claim 13, wherein said block comprises a lid component fora tunnel assembly, and said at least one third mechanical mating membercomprises two tabs provided in horizontally opposed portions of one ofsaid first side and said opposed second side of said main body portion,and said at least one fourth mechanical mating member comprises twogrooves formed in corresponding positions on the other of said firstside and said opposed second side of said main body portion.
 16. Therefractory block according to claim 13, wherein said refractory blockcomprises a wall block for a tunnel assembly, and said tab is providedin a portion of one of said first end and said opposed second end ofsaid main body portion, and said groove is formed in the other of saidfirst end and said second end of said main body portion.
 17. Therefractory block according to claim 16, further comprising at least onethrough-hole having openings formed in said first side and said opposedsecond side of said main body portion, and which is not in communicationwith said at least one cavity of said main body portion of saidrefractory block.